Prior investigations involving the use of platinum group metals in internal combustion engines have led to the development of the catalytic converter for emissions reduction. Efforts are under way to also achieve such results through better combustion conditions through engine design and fuel additives. Mechanical equipment has become one acceptable alternative to accomplish desired combustion improvements. These efforts in engine design have provided significant improvements, but the objectives of improved operating efficiency and reduced noxious emissions are difficult to achieve simultaneously.
Experiences to date with fuel additives have been less successful. For example, Lyons and McKone disclose in U.S. Pat. Nos. 2,086,775 and 2,151,432 adding from 0.001-0.085% (i.e. from 10 to 850 parts per million) of an organometallic compound or mixture to a base fuel such as gasoline, benzene, fuel oil, kerosene or blends to improve various aspects of engine performance. Included among the metals disclosed in these patents are the platinum group metals platinum and palladium. In both patents the preferred organometallic compounds are the beta diketone derivatives and their homologues such as the metal acetylacetonates, propionylacetonates, formylacetonates, and the like. The two Lyons and McKone patents state that concentrations of from 0.001-0.04%, (i.e. from 10 to 400 parts per million) are not effective to improve combustion efficiency as introduced, but may become so under prolonged use as catalytically active deposits are built up in the combustion chamber. The disclosures further state that about 0.01% (i.e. 100 ppm) of the organometallic compound is usually sufficient, once the requisite amount of catalytically active deposits has been built up, to perpetuate that amount of deposits by replacement of losses therefrom. The compounds disclosed were therefore not capable of generating any instantaneous catalytic effect at low concentrations, and in higher concentrations would provide no economic benefit. This fact is confirmed in U.S. Pat. No. 2,460,780 to Lyons and Dempsey at col. 1, lines 11-36.
The Lyons and Dempsey patent relates principally to employing catalysts which are soluble in water or other "internal liquid coolants" such as alcohol or soluble glycols or aqueous solutions of these. While catalyst levels based on the weight of metal compounds as low as 0.001% are disclosed, it is stated that for immediate catalytic effect, the catalyst compounds may be present at a level of at least 1% of the weight of the operating fuel charge. No disclosure is given of fuel soluble catalysts at levels below 0.01% or without oxygenated solvents. Moreover, where alcohol and glycols are employed with water soluble catalysts, they are disclosed principally as solublizing carriers for catalysts and for their known internal cooling function at high load.
Robinson, in U.S. Pat. No. 4,295,816, discloses an elaborate delivery system for introducing water soluble platinum group metal salts through the air intake of internal combustion engines to deliver platinum group metal catalysts to the combustion chamber at a level no greater than 9 milligrams of catalyst per kilogram of fuel. The equipment disclosed by Robinson, unfortunately, is far more complicated than would be desired for automotive operators and the water soluble salts employed, e.g. halides, have disadvantages alone or when dissolved.
In German Offenlegungsschrift 2,500,683, Brantl discloses a wide variety of catalytic metals which may be added to hydrocarbon fuels to reduce nitrogen monoxide and oxidize carbon monoxide at the moment of combustion in internal combustion engines. Among the metals disclosed are metal complexes of the metals ruthenium, rhodium, palladium, osmium, iridium and platinum, with different ligands, which can be added to the fuel individually or as a mixture. For these platinum group metals, broad concentration ranges of from 0.347 to 3.123 grams per liter of fuel are suggested for the various compositions listed in the disclosure, with the range for particularly favorable results being from 0.868 to 1.735 grams per liter of fuel. Considering the cost of these metals and the compositions containing them, there is a negative incentive for employing them at the high levels stated by the disclosure as effective. Moreover, the disclosed tetramethyl platinum compound is not known to exist.
Although the prior art has identified the platinum group metal compounds as superior catalysts for improving fuel efficiency and reducing noxious emissions, an ongoing problem has been to produce a platinum group metal compound which is sufficiently stable for packaging and delivery to the engine as well as having sufficient solubility in the fuel and insolubility in water which may be contained with the fuel. Unfortunately, nothing in the prior art has provided such compounds.